Recoil check



Feb 23, 1932 R. W, ALBERTSON HECOIL CHECK biled- Dec. 5, 1925 PatentedFeb. 23, 1932 UNITED STATES RUSSELL W. ALBERTSON, OF FORT ATKNSON,WISCONSIN RECOIL CHECK Application filed December 5, 1925. Serial No.yI"3,30.

This invention relates to improvements in recoil checks of a typeparticularly adapted for motor vehicles.

Broadly speaking, it is the principal object of this invention toprovide a n ovel and improved recoil check in which initial d1spincement between the parts connected thereby is substantially unopposcdbut in which the checking action is proportioned to the extent otdisplacement and thereby to the torce ofthe recoil. t will be understoodthat the torce with which a spring supported body will be caused torecoil will depend upon the extent of the displacement. Most recoilchecls exert a constant retarding eiiect on the recoil and consequentlydo not discriminate in eti'ect between a severe shock and a light shock.It is my purpose to provide two relatively movable members in astructure so organized to permit ot' substantially unretarded relativemovements of said inembers in one direction while checking their recoilor opposite movement to an extent which will be directly dependent uponthe extent of the displacement and will consequently be proportioned ina manner hereinafter described to the torce with which the recoil tendsto occur.

lt is also my purpose to provide a device in which the checking actionis gradiuiliy i'lecreased as the parts approach their nor-- malpositions.

I am aware that various attempts have been made more or lesssuccessfully to proportion the checking action to the displace nient. ltis, however, my object to produce this result more dependahly than hasheretofore been possible and by a principle newly realized. in thisiield, whereby the arcuate angle and area of trictional surfaces incontact actually varied in exactly the desired proportion whilemaintaining like pressures at all points of contact. By adopting thisprinciple I have succeeded in proportioning thc checking torce to thedisplacement while eliminating the possibility that the recoil checkinigl'it fail to respond to a succession of short, sharp shocks and Ihave produced a device which is dependably effective.

Further objects oi? the invention conteniplate the provision oi a simplecompact device provided with means for its ready adjustment, theprovision ot' a device wherein the friction brake mechanism has amechanical advantage over the cable which actuates it so that greatersensitiveness is achieved with less wear on the parts7 the provision ofmeans for eliminating slap and rattle during the operation of the parts,and the provision oi a device which can be `constructed to in# clude allof the aforementioned advantages and is nevertheless enclosed in asubstantially tightcase in which the non-frictional parts can be'packedin grease and which lends itself to attachment with great facility tomotor vehicles.

ln the drawings:

Figure i is a side elevation of an embodiment of this invention appliedto the frame and axle of a motor vehicle but having its cover plateremoved to expose its interior construction.

Figure 2 is a section taken on line 2-2 ot Figure l showing the coverpiate in place.

Figure 3 is a detail `View taken on the sec tion through the drumindicated at 3-3 in Figure 2.

Figure 4i is an enlarged detail showing airagn'ient of the friction drumto illustrate the relieved periphery thereof.

Like parts are identified by the saine ref- @rence characters throughoutthe several views- 1While the casing in which my improved recoii checkis housed may be of any desired character, nevertheless I prefer theconstruction illustrated for reasons which will be made apparent in thediscussion of the functions of the several parts. The casing 5 shown inthe accompanying `drawings includes a wail t5 ot ovoid outline and anout wardiy projecting wall 7 extending about the perimeter ot wall 6 andintegrally connected therewith. A boss at 8 and a stud at 9 are inodetubular to support the shaft 10 upon which the moving parts of thedevice are rotatable. A cross pin ll is preferably used to lrey theshaft l() against rotation so that it is rigidly connected with thecasing shell 5. Journalled upon the shaft 10 is a rotor l5 sinpreferably provided with a roller bearing 14 fitted therein.

The rotor includes differentially diametered drum portions 16 and 17 tobe described later. A thrust nut 18 threaded to shaft 10 bears againstthe bearing 14 and has been found to be adapted to take end thrustwithout'noise. Fine threads are used to connect nut 18 with shaft 10 sothat a very accurate acglustment is possible. A pin 18 is used to securethe parts in the desiredadjustment.

The casing shell V5 and the rotor 15 are provided with complementaryarcuate ribs 19 and 20, respectively. The extent of these ribs is shownin Figure 3, and it will be observed that they are not quite annular butare provided with spaced ends 21 and 22, thetwo ribs being alike in thisparticular. These ribs provide seats for the ends of the torsion spring.25 which has hooked extremities 26, each of which is engaged about oneof the ends of one of the arcuate ribs above referred to.

In practice, the spring 25 is maintained under torsion tending to rotatedrum 15 upon the axis shaft 10 of the casing shell. A cover plate 27conforming in outline to the casing shell and provided with a circularopening receiving the drum portion 16 lof rotor 15 is secured to thecasing and encloses drum portion 17 and the friction brake mechanismhereinafter to be described.` A rubber gasket at- 28 makes asubstantially grit-proof closure between the cover plate 27 and theshoulder 29 of the rotor. A flange 30 on the cover plate embraces theperiphery of wall 7 of the casing and -makes a tight joint therewith. Aboss 31 cast integr"L ily with the wall portion 6 ofthe casing isadapted to receive a screw 32 whereby the cover plate is detachablysecured in place.

The drum portion 16 of the device may be made concentric with shaft 10and is adapted to have wound thereon a vtension member 35 which, for thepurposes of the present disclosure, comprises steel cable having at itsfree end a headed fitting 36 adapted to be engaged by a clamp member 37on the axle 38 of the vehicle. At its other end the cable 35 carries afitting 39 of the peculiar form best shown in Figure 3 and so designedas to provide a bent arm 40 which may be manipulated t irough anopeningl1 in drum portion 1G of the rotor and is adapted to interlock with therotor in such a manner that it cannot be withdrawn from opening 41 aslong as 'the tension member 35exerts a pull substantially tangentialwith reference to the rotor. The torsion of spring 25 keeps the cable 35constantly under tension so that when the casing 5 ('wliicn isunderstood to be bolted to the vehicle frame) approaches the vehicleaxle 38 the torsion spring will rotate the rotor '15 to wind cable 35 ondrum surface 16 and thereby to take up all slack therein. The extent ofrotation permitted to the rotor 15 by cable 35 will obviously beproportioned to the extent to which the vehicle frame and axle approacheach other.

While it is broadly immaterial whether the drum surface 16 be concentricor eccentric with reference to the'axle shaft 10 it is very important tothe present invention that the brake drum surface 17 be provided with aperipheral portion of reduced radius. For the purposes of this inventionthe otherwise concentric periphery of the brake drum 17 is relieved at113 to provide a peripheral portion of less radius and of substantiallygreater than 90 extent in the present embodiment of the invention. Theperipheral extent of the relieved portion 43 of the brake drum ispreferably so determined as to approximate the maximum range of rotordisplacement.

Interacting Vwith the friction drum surface 1 17 is a shoe 50 which maybe slightly flexible but which, comparatively speaking, is rather rigid.1n practice this shoe has been satisfactorily made of a band 51 of 16gage steel faced at`52 with a leather lining. The friction shoe isconcentric with the axis of shaft 10 and is anchored at 53 to theinterior of wall 7 of the Casing shell 5. At its free end the shoe 50 isconnected with a yoke'55 which is slidable upon a screw 56. The angle ofconvergence between the sides of wall 7 of the casing is so determinedthat the head 57 of screw 56 will be in plane Contact with the exteriorsurface of wall 7, whereby the screw may be readily rotated in theaperture 58 in said wall. A nut 59 is threaded upon screw 56, and acompression spring 60 coiled about screw 56 is confined between nut 59and the end of yoke 55. By rotating screw 56 it is possible toadjust thetension exerted Aby spring 60 upon the friction shoe 50, and obviouslysuch tension will be determinative in a general way of the pressure withwhich the leather facing 52 will initially be forced into contact withthe periphery of, drum portion 17 of the rotor. The band 51 has anarcuate form concentric with shaft 10, and its slight degree ofpliability is adequate to enable itto accommodate itself to the surfaceof friction drum 17 sufficiently to distribute over such drum thepressure to which it is subjected by spring 60. l The flexibility ofband 51, however, is not vsuch as tov cause such band to deviatematerially'frorn its original arcuate form'whenthe relieved portion 'itsl second factor varies at a variable rat-e.

43 of the drum passes therebcneath. It is obvious, therefore, that therewill be no fric tion whatever between the shoe and that part of therelieved periphery 43 of the drinn which underlies the lining 52 of theshoe 50.

lf desired, the device may be designee to cnsnre against deviation ofthe band from its normal arcuate form. This may be done by interruptingtle continuity of relieved portion 43 with a bearing protubcranee li"corresponding in radius to the brake surface 1T. This supports the brakeband or shoe and facilitates pre-calculati m of the operation of thedevice by keeping the shoe inflesed and thus allowing spring GO toremain at constant tension. The spring (SO tends to bccome overloaded inany event and it is desirable to lreep it under as nearly constanttension as possible.

It has long been lrnown that a. shoe which is anchored rigidly at one ofits ends and is rcsiliently anchored at the other end about a frictiondrum will bind itself upon the drum when the periphery of the drumrotates away from the anchored end of the shoe, whereas when the drumrotates toward the anchored end of the shoe the initial frj'zctionalContact between the drum and shoe will cause the shoe to yield and leavethe drum practically free for its subsequent rotation in that direction.ln the present device the springl GO yieldably anchors one end of shoe50 and, conscqnently, when the rotor l5 is turned in a clockwisedirection viewed in Figure l nn der torsion of spring 25, its rotationwill be practically nnopposed by any friction between the drum and theshoe 50. lWhen, hmvever, the drum is caused to be rotatedcounter-clockwise by recoil in the vehicle spri ng which is interposedbetween the frame and axle to which the drum casing and cable arerespectively connected, the result will be to draw shoe aga-inst itspositive an chorage at 53, whereby it will be caused to bind on theperiphery of the friction drum l? and to check 'the recoil.

In a general way the binding effect in the presentdevice will beproportioned to:-1, the initial tension of spring 2, the arcuate l angleof contact between the band and drum;

and 25, the area of contact; el, the character of the frictionallyrelated surfaces. The first and fourth factors are constant duringnormal operation of the present device. The The third factor varies at asubstantially constant rate.

It will be remembered that in the normal position of the parts as shownin Figure l,

` the relieved portion i3 of the friction drum underlies a comparativelylarge extent of the shoe 50. The area of friction surface between thedrum and shoe is at a minimum in this position of the parts. lfdisplacement now occurs between casing and the parte to which cable 35is connected the drum will rotate in a clockwise direction, and whilethe drum encounters no material degree of friction in opposition to thisclockwise rota-l tion, nevertheless it will be observed that the angleof contact and also the potential friction area is being increased inexactly the proportion in` which displacement occurs be` tween theparts. angie and area is produced by the movement of the relievedportion 43 of the drum out from under the friction surface of the shoe50. At the maximum displacement to which the parts areordinarily subjectthe relieved por.- tion of the drum will have passed wholly from beneaththe friction surface of the shoe, and the drum will be in a position forfrictional contact with the entire length of the friction surface of theshoe. It is particularly to be noted that the arcuate space between theend 61 of the line 52 and the end 62 of such lining is so calculatedthat the relieved portion 43 of the drum will not pass beneath end G2 ofthe lining until it has left end 61 thereof.

finer displacement has occurred and a greater. or less portion of therelieved periliiheryt3 of the drum has passed from beneath the shoe 50the recoil will take place and, from the above discussion, it will` beap preciated that such recoil will be opposed by tl e oinding of theshoe on the periphery of the drum. The degree of opposition to therecoil or counter-clockwise rotation of the friction drum will be in ageneral way proportionate to the original displacement. lt will not,however, be exactly proportioned to the displacement but will tend toincrease more rapidly than 'the value of the displace ment and with aconstantly increasing factor. Se far as the area of surfaces infrictional contact concerned, the binding effect and con sequentchecking action will. probably be directly proportional. As` the`included" angle of frictional contact increases, however, there is anincreasing factor of potential checking action due to the development ofa snubbing effect.

lt follows from the foregoing remarks that the recoil check hereindescribed will offer comparatively little resistance to recoil when 'thedisplacement has been slight, butthat a high resistance will beinitially offered to recoil when` the displacement has been greater,Ubv'iously, the high resistance which is in v offered subsequent to acomparatively displacement decreases as the displacenient decreases andreaches a minimum value when the parts have been restored to theirnormal positions.

@ne situation remains to be considered. If

the displacement of the drum is so excessive as to bring the relievedportion 43 thereof beneaththe free end 62 of the shoe the result will bethat when recoil commences the de- Ubviously, the increase in CLL vicewill not act initially with its maximum retarding eect. This isdesirable since in cases of extreme shock the retarding effect would betoo severe if it were increased in the proportion which the increasefollows during the normal operation of the parts. The constructionillustrated, however, is such `that when the parts exceed their normaldisplacement the area of the friction surface becomes 1 decreased, andduring recoil the resistance will be somewhat below the maximum at firstand will reach the maximum when the parts reach their maximum normaldisplacement. This action of the checking device results in graduallyabsorbing the. shock and after the present embodiment of the inventionthe friction surface of the drum and also that of the shoe each `has anarcuate extent of approximately two-thirds of the entire periphery ofthe drum. These proportions need not be adhered to but have been foundsatisfactory in practice.

The length of tension member is preferably so adjusted that the relievedportion of the drum will, in the normal stationary positions of theparts, underlie the fixedly anchored end of the brake. The reasons forthis have already been explained. It may be said, however, that theeective length of the tension member or cable may readily be variedthrough the simple expedient of providing a number vof apertures 41 indrum portion 16. This not only provides means for fitting the length ofthe cable to the dis-- tance in any given installation between a vehicleaxle and vehicle frame but, furthermore, the adjustment of the cableprovides means for taking care of variations in the stiffness of thevehicle springs. It will be obvious that if the cable is `so adjusted asto increase its length over that indicated in Figure 1 so that the drumis permitted to rotate clockwise, the change in initial position of thedrum will increase the initial intensity of the checking action of thedevice. The construction illustrated is such that a minimum checkingaction will occur during those minor os-.

l checking action throughout the range of operation of the device. It iswell known in the art that the adjustment of the tension of such springsaffords means for controlling the braking effect which will be exertedby the shoe when the drum rotates from the fixed anchorage of the shoetoward its yieldable anchorage.

While the device thus far disclosed is a complete and operativestructure, for the purposes of this invention I prefer to add one ormore stops shown at as comprising studs projecting inwardly from thecasing 5. These stops positively limit the releasing movement ofintermediate portions of the band. Because of wide variations in leatherthickness, I prefer in practice to adjust each stop separately by makingit in the form of a screw which will be turned down tight on the bandand an interposed shim. A shim .005 inch more or less will besatisfactory considering the self-compacting quality of the leatherused. The shim is now withdrawn and the screw sheared off to leave thestu-d 7G, or inner end of the screw in the desired position as indicatedby experiment. Stops 70, however, serves to relieve the device of anannoying slap to which other recoil checks are subject upon suchoccasions as are frequently encountered in practice where a series ofshocks reach the device to cause it to act several times in quicksuccession. Under suchcircumstances the friction band or shoe of theordinary recoil check frequently leaves the drum to such an extent thatwhen the slack is taken up there is a pronounced slap very annoying tothe operator of a vehicle equipped with such a device. By using a stop70 extending into close proximity to the band I have overcome theobjectionable slap without in any way interfering with the operation ofthe device.

In stating the objects of this invention I mentioned the fact that Idesired to give the friction mechanism a mechanical advantage overthe'tension device or cable 85. The desired result is accomplished bymaking the drum portion 16 of the rotor somewhat smaller than thefriction surface 17. frictional resistance on surface 17 to check agiven amount of recoil than would be necessary if the surface 17corresponded in its radius to surface 16 of the rotor. At the same time,the sensitiveness of the `device is increased inasmuch as acomparatively slight movement of cable will produce a correspondinglyincreased linear travel on the surface of friction drum 17. It isfurthermore to be noted that the shoulder between the two drumsco-operates to good purpose with the closure plate Q7 to exclude foreignmatter from the interior of the casing. It is very important that waterbe excluded because water changes the frictional characteristic of theleather or other brake lining employed at 52 on the friction shoe. Thefact It takes lessthat the two drums l? and 16 are integrally connectedin a common hollow rotor affords desired room for a torsion spring ofample size for the operation of the device.

l claim:

l. ln a device of the character described, the combination of tworelatively movable members of substantially fixed contour hav ingpartially overlapping friction surfaces in their normal positions, meansfor maintaining said members in frictional engagement, means formounting said members for relative movement aforesaid while maintainingsuch frictional engagement, and means for moving one of said memberswith respect to the other whereby to vary the extent of overlap betweenthe respective friction surfaces of said members.

2. ln a device of the character described, the combination with a rotorhaving a braking surface, of a shoe frictionally bearing on suchsurface, such surface being relieved to provide a portion of said rotorout of contact with said shoe and of a length such as to be adapted tobe spanned thereby, whereby the rotation of said rotor is adapted tovary the included angle of frictional contact between the brakingsurface of said rotor and that of said shoe.

3. In a device of the character described, the combination with abraking shoe providing a discontinuous braking surface, of a rotorsupported for oscillation adjacent said surface and provided with aportion of such extent that some part thereoef will underlie saidsurface in all positions of said rotor in contact frictionally with said.surface and a relieved portion spaced from said surface, theoscillation of said rotor being ladapted to vary the frictional area ofcontact between said rotor and said shoe.

el. In a device of the character described, the combination with amember having a peripheral surface with portions at different radialdistances from its center, of a brake shoe operatively associated forfrictional contact with said member and supported by relativelyyieldable and fixed anchorages at its respective ends in such a manneras to leave said member substantially fr-ee for rotation in onedirection while opposing a variable frictional resistance to therotation of said member in the other direction.

5. In a device of the character described, the combination with afriction drum member and another member, said members being arranged forrelative movement, of a friction shoe connected with said other memberand supported in operative engagement with said drum, and meansanchoring said shoe to oppose frictionally the relative rotation`between said members in one direction while permittingr the freerotation between said members in the opposite direction, the said drummember having peripheral portions at varying radial distances from itscenter, whereby to vary the effect of said shoe in opposing relativerotation between said members in said first mentioned direction.

6. ln a device of the character described, the combination with a drumhaving its periphery divided into friction and nonfriction surfaces ofdiffering radii, of a friction band encircling said drum and provided atone end with a comparatively fixed anchorage and at the other ene with acomparatively veilding anchorage, together with means for producingrelative rotation between said drum and band.

7. ln a device of the character described, the combination with a drumhaving a discontinuous peripheral friction surface and an intermediateperipheral surface of lesser radius and a housing for said drum, saiddrum and said housing being relatively rotatable, of a friction strapanchored withinsaid housing passed about saiddrum and yieldablyconnected again with said housing, whereby said strap is adapted topermit substantially unrestrained rotation between said drum and housingin onedirection and to frictionally oppose relative rotation in theopposite direction to an extent generally proportionate to the extent ofthe original rotation.

8. In a device of the character described, the combination with a drummember having a peripheral friction surface interrupted by a surface oflesser radius and a housing member for said drum, one of said membersbeing adapted for connection with a motor vehicle axle and the otherwith a motor vehicle frame in a manner adapted to produce relativerotation between said members cominensurate with displacement occurringbetween said aXle and frame, of torsion means operable to producerelative rotation `between said members in one direction, a frictionshoe operatively co-acting with said drum and provided with a fixedanchorage to said casing at the end toward which a given point on saiddrum moves after frictionally contacting said shoe during the relativerotation between said members, and a yieldable anchorage for the otherend of said shoe.

9. In a device of the character described, the combination with a pairof relatively movable members having complementary friction surfaces inoperative contact and partially overlapping in the normal positions ofsaid members, of a spring housed within and acting upon one of said.members and adapted to produce relative movement between said membersin a `direction such as to increase the extent to which said surfacesoverlap, means for maintaining said surfaces in operative frictionalcontact throughout the extent of their overlap, and means actingpositively upon one of said members in opposition to said spring torestore said members to their said normal positions.

CII

10. In a device of the character described, the combination with a rotorprovided with la discontinuous peripheral braking surface, of an arcuateshoe provided with a discontinuous braking surface complementary to thatof said rotor and in contact therewith insofar as said surfaces overlap,variable means normally maintaining said rotor in a position in whichits braking surface partially overlaps the friction surface of saidshoe, and a spring acting o-n said rotor to increase the extent offrictional contact between said surface when said means fails to operateto maintain said rotor in its aforesaid normal position.

11. In a device of the character described, the combination witha rotorprovided with a discontinuous peripheral braking surface, of a-V shoecomplementary to said rot-or and provided with a discontinuous frictionsurface in contact with said braking surface insofar as said surfacesoverlap, said shoe having one of its ends rigidly anchored and anotherof its ends yieldably anchored together with means acting to producerelative rotation between said shoe and said rotor and adapted tomaintain said rotor in a position wherein the friction surface of saidshoe will partially overlap the braking surface of said rotor, theyieldable anchorage for said shoe being so disposed as to release saidshoe from binding engagement with said rotor when said rotor moves in adirection to increase the extent to which said surfaces overlap.

12.. In a device of the character described, t-he combination with arotor having a discontinuous braking surface relieved throughout amaterial portion of the periphery of said rotor,y of a shoecomplementary to said rotorand provided with a discontinuous frictionsurface in overlapping engagement with a part of said braking surface inthe norma-.l position of the parts, and a spring normally acting tomaintain said surfaces in contact, said shoe having a. suiiicientrigidity to. span the cut-away portion of said rotor and having'sufcientflexibility to be drawn by said spring into conformity with the b-rakingsurface of said rotor'.

13. In a device of the vcharacter described, the combination with arelatively fixed casing, of a rotor operatively mounted for rotationwith respect to said casing and having a drum portion in said casingwithv a part of its periphery reduced in radius and a concentric drumportion exterior of said casing, acover plate for said casing applied tosaid rotor intermediate its drum portions aforesaid, friction meansapplied to said drum portion within said casing and productive ofresistance proportionate to the degree of contact therewith in therotation of the drum portion exterior to said casing.

14. In a device of the character described, the combination with arelatively fixed cas` ing, of a rot-or operatively mounted for rotationwith respect to said casing and having a relieved friction drum portionin said casing and a winding drum portion exterior to said casing, a.cover plate for said casing applied to said rotor intermediate its drumportions aforesaid, friction means applied to said drum portion withinsaid casing and productive of resistance proportionate to the degree ofcontact therewith in the rotation of the drum, and actuating meansapplied to said drum portion exterior to said casing, said actuatingmeans comprising a cable drawn upon said winding drum portion andadapted when subject to tension to rotate said rotor in one direction,said rotor being provided interiorly with a torsion spring housedbetween said rotor and said casing and tending to rotate sai-d rotoropposite to the` direction in whichsaidrotoris turned by said cable.

15. In a device of the character described, the combination with ashallow casing and an axle shaft therein, of a hollow drum havingportions of different diameters and operatively mounted for rotation onsaid shaft, the larger portion of said drum being housed within saidcasing and the smaller portion of said drum being exposed exteriorly ofsaid casing, a brake shoe rigidly connected at one of its ends with theinterior of said casing and extending about said drum toV a, resilientlyyieldableanchoragey of` its other end to said casing, a torsion spring.connected with said casing and the outer end of said drum and housedwithin said drum, and tension means opposing the'action of said springand wound upon said drum in a direction to rotate it from the fixed endof said shoe toward the resilient anchorage thereof, the larger portionof said drum being relieved whereby to affordclearance between a por--tion of its periphery and an overlying portion of said shoe, an area ofsurface infric-- tional contact between said shoe and said drum beingvariable in accordance with the position of rotation of said drum.

16. In a device of the character described, the combination with a drumhaving approximately one-third of its periphery cut away to reduce itsradius and having the remainder of its periphery substantiallyconcentric with its axis, a shoe provided with a friction surfacesubstantially the arcuate extent of the concentric portion of theperiphery of said drum, means supporting said shoe in a positionaffording operative frictional contact between said surface and theperiphery of said' drum, and means for producingrelative rotationbetween said shoe and said drum, said rotation beingV adapted to varythe a-ngle of friction contact between saidshoe and said drum byvaryingthe ex- Clt tent to which the friction surface of said shoeoverlaps the concentric peripheral portion of said drum.

l?. In a device of the character described, the combination With a drumhaving approximately one-third of its periphery cut away to reduce itsradius and having the remainder of its periphery substantiallyconcentric with its axis, a shoe provided With a friction surfacesubstantially the arcuate extent of the concentric portion of theperiphery of said drum, means supportingr said shoe in a positionalfording operative frictional contact between said surface and theperiphery of said drum, and means for producing relative rotation'between said shoe and said drum, said rotation being adapted to varythe area of friction contact between said shoe and said drum by varyingthe extent to Which the friction surface of said shoe overlaps theconcentric peripheral portion of said drum, said means beingl adapted tomaintain said drum and said shoe normally in relative position such asto maintain a minimum degree of such overlap.

18. In a device of the character described, the combination with acasing, of a friction shoe having an arcuate extent of approximately211: and provided at its opposite ends with relatively fixed andrelatively yieldable anchorage to said casing, a drum positioned withinsaid slice and provided with a periphe 'al friction surfacesubstantially corresponding in extent to that of said shoe and relievedthroughout the remainder of its periphery to avoid contact With saidshoe, and means for actuating said drum to oscillate it with referenceto said shoe, said means being adjusted normally to maintain said drumin a position in which a minimum port-ion of its periphery Will overlapthe frictional surface of said shoe, the relieved portion of theperiphery of said drum underlying the end of said shoe Which is providedWith a fixed anchorage whereby any displacemeiit of said drum willincrease the opposition to a movement of said drum from said fixedanchorage toward said yieldable anchorage.

19. In, a device of the character described, the combination with a drumhaving' a peripheral friction surface interrul'ited by a relievedportion of less radius, of a shoe conforming' to the friction surfaceportion of said drum and adapted to span the relieved portion thereof,said shoe being provided with a relatively lixed and a relativelyyieldable anchorage at its respective ends, a tori-tion spring actingnon said drum in a direction to rotate it toward the fixed anchorage ofsaid shoe, and positive motion transmitting connections acting,` on saidnrum in a direction to rotate it from the fixed anchorage toward theyieldable ancho-rage of said shoe, said connections being normally soadjusted that When the parts are at rest substantially the entirerelieved portion of said drum Will underlie that end of said shoeadjacent its fixe-d anchorage.

20. A recoil check comprising the combination of relatively rotatableparts having relatively discontinuous friction surfaces adapted forinteraction in opposition to the relative movement of said parts towarda predetermined relative position, said surfaces being so disposedy withreference lto said position that their mutua-l overlap varies generallyproportionately With displacement throughout a tgiven range of relativerotation to and from said position and generally in versely as thedisplacement in excess of .aid

range. w

2l. A recoil check comprising thecombination of relatively rotatableparts having relatively discontinuous friction surfaces adapted forinteraction in opposition to the relative movement of said parts towarda predetermined relative position, said surfaces being so disposed withreference to said position that their mutual overlap varies generallyproportionately kwith displacement throughout a given range of relativerotation to and from said position and generally inversely as thedisplacement in excess of said range, the frictional resistance torelative movement toward said position being approximately in accordanceWith overlap of said surfaces whereby such resistance vvillprogressively increase in approaching said range and progressivelydecrease within said range.

22. A friction check comn'ising the combination of a rotatable memberhaving a discontinuous friction surface, and an arcuate shoe memberhaving a complementary discontinuous friction surface and mounted tooppose drum rotation frictionally, the extent and posit-ions of saidsurfaces being so determined that their maximum degree of overlap willoccur intermediate the extremes of possible relative movement.

23. T he combination with relative rotatable members, of an arcuatesurface on one thereof, a friction shoe in pressure engagement aboutsaid surface and anchored at one of its ends to the other of saidmembers, whereby frictionally to oppose relative rotation of saidmembers in one direction, and one of said members having a contour forrelieving the degree of initial opposition offeredby said shoe when saidmembers have exceeded a predetermined displacement.

24. The combination With relatively rotatable members and a springtending to rotate them from a predetermined initial p0sition, of acurved peripheral surface limited in arcuate extent upon one of saidmembers, and a friction shoe under tension about said surface andanchored at" one of its ends to the other of said members, wherebyfrictionllO ally to oppose relative rotation of said members toward saidposition only, said shoe and surface having relatively little overlap insaid posit-ion and being of such relative extent as to reach a maximumdegree of overlap before reaching maximum displacement from saidposition.

25. The combination With a rotatable member having its peripheryrelieved to provide a discontinuous friction surface concentric with theaxis of rotation of said member and of relatively greater radius thanadjacent portions ofthe periphery thereof, of a relatively fixedhousing, a flexible brake shoe anchored at on-e end Within said housingencircling a portion of said member and yieldably connected at its otherend with said housing, said shoe being extended about only a portion ofsaid member, tension means adapted to rotate said member in oppositionto the friction of said shoe, and a spring connected between said memberand said housing adapted to rotate said member in the oppositedirection, said tension means being so adjusted as to maintain therelieved portion of said member normally Within the compass of said shoeand in a position to pass from beneath said shoe upon rotation of saidmember by said spring.

26. The combination Wit-h a rotatable member having its peripheryrelieved to provide a discontinuous friction surface concentric With theaxis of rotation of said member and of relatively greater radius thanadjacent portions of the periphery thereof, of a relatively fixedhousing, a flexible brake shoe anchored at one end Within said housingencircling a portion of said member and yieldably connected at its otherend with said housing, said shoe being extended about only a portion ofsaid member, tension means adapted to rotate said member in oppositionto the friction of said shoe, and a spring connected between said memberand said housing adapted to rotate said member in the oppositedirection, said tension means being so adjusted as to maintain therelieved portion of said member normally Within the compass of said shoeand in a position to pass from beneath said shoe upon rotation of saidmember by said spring, the proportion and arrangement of the parts beingsuch that in an extreme rotative position of such member under theaction of such spring, the

- relieved portion of said member Will pass beneath another portion ofsaid shoe.

27. A recoil check comprising the combination of relatively rotatablemembers, and means for frictionally opposing rotation of said memberstoward a predetermined relative position, said means and a member beingfrictionally engaged and mutually spaced for a predetermined.peripheralextent Whereby to be adapted to produce a frictional opposition variablein intensity according to the displacement of said members and adaptedtoI reach a maximum intermediate the range of possible displacement. l

28. A friction check comprising members relatively rotatable between aneutral position and an extreme position, and means opposing a variablefrictional resistance to the movement of said members toward saidneutral position and controlled in the relative movement of saidmembers, said means andone of said members having partially relievedfrictionally engageable surfaces angularly positioned for a maximumengagement at an intermediate point in relative rotative movement ofsaidmembers and operatively adapted to afford frictional oppositionreaching a maximum at said point, whereby `said members in their extremepositions Will be opposed by frictional resistance gradually increasingto said maximum and thence decreasing toWard a "minimum in approachingsaid neutral position. l

RUSSELL W. ALBERTSON.V

